Also clear gitpod user's Go build cache

The go clean -cache only clears root's cache. The golangci-lint
install runs as USER gitpod and hits stale go1.24.9 objects in
/home/gitpod/.cache/go-build.

Co-authored-by: Ona <no-reply@ona.com>

Author: geropl

dev/image/Dockerfile

@@ -16,7 +16,8 @@ RUN rm -rf /usr/local/go \
     && curl -fsSL "https://dl.google.com/go/go${GO_VERSION}.linux-amd64.tar.gz" | tar -C /usr/local -xz \
     && ln -sf /usr/local/go/bin/go /usr/bin/go \
     && ln -sf /usr/local/go/bin/gofmt /usr/bin/gofmt \
-    && go clean -cache
+    && go clean -cache \
+    && rm -rf /home/gitpod/.cache/go-build
 ENV PATH=/usr/local/go/bin:$PATH
 
 ### cloud_sql_proxy ###